On our network we have two dns servers, and the first 50 IP addresses are static while everything else uses DHCP.

Since I haven't been the "IT Guy" here since this network's original setup, I am not sure which devices are on which static IP addresses, and which static IP addresses are free for the taking.

I realized this yesterday when I went to set up a new printer. I didn't know which static IP addresses were currently being used, and decided to set the printer up as DHCP with a reservation to prevent problems from address changes.

While, for this situation, DHCP worked fine, I realized that there will be times when I cannot use DHCP to accomplish a goal - so I am curious if there is a way to view claimed and available static IP addresses easily. I went into our DNS server's DNS settings and poked around, but didn't know if numbers I was seeing there were accurate, since some of the devices listed have not been used in a very long time.

I also ran an NMap scan, which is a great way to find device IP addresses for machines that are On, but I'm worried it will miss something.

Again, it's only the first 50 IP addresses available for static use, so if worse comes to worse I can start tracking down physical computers/appliances/printers/etc and figuring out exactly which is which, but that seems like a gigantic pain in the ass and that there should be an easier way.

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Spiceworks Network Scan might help, provided you can link it to AD or provide admin credentials that work on all those machines. Then you can just automate the process and go through the device list later.

Thanks for the recommendation, but I already use Spiceworks (obviously ^^). The Spiceworks scanning has been unreliable on our network in the past and I've had to manually add machines and alter the 'automated' results of the scans. AD doesn't contain a clearly organized representation of our network, but because of the way our scripts are laid out I cannot alter our layout without a significant amount of work. Our layout and scripts work fine, so I'm in no rush to change it, but in this particular case I don't believe Spiceworks is the best tool for the job.

I often use a program called Angry IP Scanner to see what is active. I operate under the assumption statics are assigned to servers, network hardware, and printers and should be always on. Mistakes happen, but the IP scan gives me a first glance at the usage.

Here is what I would do you have list of IP's write a batch file to ping each IP once find all the active IP's. From a dos prompt do an arp -a this will give a list of all the IP's and MAC's copy this to notepad. You can also do similar commands on managed switches and in some routers. Create reservations in DHCP for these so now you have list. Even if the device changes you will be the one changing it so give it the same IP and your list is still correct.

Use excel put this string in the first box drag down to as may as you want to do

ping xxx.xxx.xxx -n 1 copy and paste into a dos prompt do an arp -a copy results to notepad and if you format them correctly they can be imported into DHCP as reservations.

For stuff like this I always liked an old program called Look@Lan, once you create a range it remembers the computers it found. I'd run it a couple times a day over a period of time to see if any other machines came online. If thats not reliable enough, the manual way is the only other solution I can think of.

Another idea is to put the addresses you find into DHCP as bogus reservations (use all 0s for the mac) this way you know what they are in the future.

If I go into DNS, I can click "Reverse Lookup Zones". From there I can click my subnet, for example, "10.0.0.x Subnet". This will return a list of IPs used and the name they are pointed at.

How reliable is that data? Is there a way I can forcefully "renew" that data, so that machines that have not connected on those IPs in say, a week, a month, or a year, will be "freed" up, or removed from the listing?

Also, I see numbers go from say, 10.0.0.9, to 10.0.0.12, does this mean that 10.0.0.10 and 10.0.0.11, NOT BEING LISTED are safe to use - or is there some chance that those numbers are being used on machines/appliances and just not showing up?

To me, if this works, seems far more logical for "static" machine IPs than relying on currently-live-machine-scanning software, especially if I'm off-site.

DNS may not be your best friend here, its only going to list the devices that were put in manually or that registered, unfortunately devices like switches or printers with static IPs assigned locally will usually not register.

That's what I was afraid of, I wasn't sure if they would all automatically show up there once an IP was used, or if not. I guess I'll use those DNS records to compare against what I turn up from an Nmap & look@lan scans, then do a manual "Easter Egg Hunt" in our company for all of our odd-ended, non-computer equipment that might have a manually entered IP and figure out if there are any conflicts, jot everything down, and just make sure I keep records up to date manually so we don't have this problem in the future. Sometimes I wish our old admin had kept track of things better - I mean, I understand a lot of it he had stored away in that brain of his, but picking up where he left off is exceedingly annoying at times.

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